Environment variable
aka: env varaka: .envaka: secret
The Quick Version
A configuration value stored outside your code.
How it actually works
Environment variables are key/value pairs injected at runtime. Locally they live in a .env file that is never committed; in production you paste them into your hosting dashboard. Server-side ones stay private; anything exposed to the browser is public by definition.
Why does it matter?
It is how you use passwords and API keys without hard-coding them into a public repository.
Example
DATABASE_URL=postgres://…